Pseudorotaxane formation affected by stereo-electronic effects. A theoretical and experimental study

PORASSO, RODOLFO D.; SANCHO, MATIAS I.; PARAJO, MERCEDES; GARCIA RIO, LUIS; ENRIZ, RD

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2022

1463-9076

We report a theoretical-experimental study on different complexes of pseudorotaxanes possessing pyridine axles. In order to evaluate the stereo-electronic effect of the methyl substituents in the pyridine ring, complexes with different substitution patterns were synthesized. In this way it was possible to analyze the different behaviors of these complexes according to the positions of their methyl substituents. Combined techniques of molecular dynamics and quantum mechanical calculations with the help of molecular electrostatic potentials for a simpler visualization of the electronic effects were employed. We have sought experimental support on NMR spectroscopy analysis to corroborate the conclusions obtained from the molecular simulations. Our results clearly demonstrate that both electronic and steric effects play a key role not only in the feasibility of formation of such complexes, but also simulations reported here might predict the degree of difficulty of their formation. Combination of computational techniques employed here seems to be an excellent approach to be able to predict whether or not a complex can be formed and with what degree of difficulty. In addition, our experimental and theoretical results have allowed us visualization of the formation of external complexes in the rotaxanes reported here. In this case, the use of bolaforms with trimethylammonium groups in both ends was very useful to evaluate in details the formation of the so-called external complexes in these systems.